Cumulative Hydrological Effects Simulator (CHES)


CHES (Cumulative Hydrological Effects Simulator) estimates the net changes to the flow regime throughout a catchment due to multiple water use schemes. It also quantifies the consequences for both the overall availability and reliability of the water resource and the residual flows that determine the in-stream environmental effects such as physical fish habitat availability.

CHES provides water resource managers with cost-effective, rapid, and flexible assessment of the cumulative effects of complex surface water allocation scenarios. It can even incorporate future climate change.


NIWA's new CHES (Cumulative Hydrological Effects Simulator) software tool predicts how water flows in a catchment will change with multiple water uses (e.g. direct abstractions or storage reservoirs) and what the consequences will be to in-stream ecosystems and reliability of water-take.

CHES is easy to use and an essential tool for understanding the interplay of existing and new abstractions. It enables you to analyse the simulated or measured time series of residual river flows, and water takes, for user-specified scenarios.


 User Interface - Guide to the main CHES window.


CHES can simulate the following abstractions:

  • “take” (simple abstraction from the river),
  • “off-line dam” (water is abstracted from a river via an external dam, which acts as buffer), and
  • “dam” (an in-line dam, e.g., Clyde Dam).

CHES is catchment-based, and can generate surface water flows and dependent attributes as catchment averages, reach averages and reach time series. It requires the mean daily, natural flow time series to be supplied for each reach of the catchment that is to be examined.

CHES incorporates modelled river-flow time series for New Zealand's half-million reaches, and includes user-specified abstraction and storage options. It calculates the effects of water use by combining numerical water routing with operating rules. For example, placing a dam into a catchment uses a digital elevation model to calculate reservoir geometry and storage dynamics.

Data requirement
There are a number of data requirements to run CHES in the ArcGIS environment, these can be divided into the following four groups:

  • ArcGIS layer: data needed for the visualization within the ArcGIS software.
  • CHES data: data needed to run the CHES simulation.
  • CHES additional data: additional metadata needed to run the CHES simulation (NIWA supplied).
  • Model data: metadata needed to estimate the desired indices from the supplied models.

The ArcGIS data layers required include: existing takes,  new takes, storage dam,  streams, DEM and HydroEdge. Much of this data can be supplied by NIWA. The specific data required to run the CHES simulation includes flow data, slope, REC meta data and other reach parameters, again much of this is supplied by NIWA.

Latest Version CHES 4.1 for ArcGIS 10.6 (June 2018)
State of Development Released and updated

Development Contact

Dr James Griffiths

Main Developers

  • National Institute of Water and Atmospheric Research (NIWA)


Outcome Areas Environmental
Management Domains Freshwater
Subdomains Water Quantity/Flows, Water Yield
Intended End Users
  • Regional Council Scientist
Spatial Resolutions 10-100m
Spatial Extents Local (i.e. Catchment or District)
Spatial Dimensions 2D
Temporal Resolutions Years
Temporal Extents Years
Steady State or Dynamic Unknown
Level of Integration Environmental

Input & Output Data

Key Input Data Runoff, Land Use water allocation data, digital river network, ecological data
Input Data Formats XLS(X), CSV, GIS compatible files
Key Output Data Water quantity - reach-scale flow estimates under different water allocation scenarios
Output Data Formats CSV, Image File(s), GIS Compatible Files


Open/Closed Source Closed Source
Licence Cost
Price negotiable

User Information

Operating Systems MS Windows
Software Needed ArcGIS Need ArcInfo Desktop and Spatial Analyst licences
User Interface Graphical desktop
Ease of Use Moderate
Use in Policy Process Plan (Policy Formulation), Review (Issue Identification)

CHES Manual - Draft (2018)

Support Contact
Users Forum Information updates to registered users

Technical Considerations

Programming Language
Methods included for managing uncertainty In the simulation of flow time series data the option is available to set the level of uncertainty at 'low' or 'high' to provide a second flow time series in addition to the 'best estimate'.
Analytical Techniques Input/output
Keywords Water allocation, scenarios, water resource management
Linkages to other Models

CHES - smarter use of New Zealand’s river waters: (

Managing water allocation on the West Coast:   (

Key References

 Hoyle J, Diettrich J and Franklin P. (2016): Applying the Cumulative Hydrological Effects Simulator (CHES) for managing water allocation: A demonstration of CHES in the Grey catchment, West Coast. Prepared for West Coast Regional Council.





Associated Case Studies

CHES - Grey River Catchment West Coast

This tool can be used to provide support to the management decisions on water allocation in a spatially complex region which experiences diverse water uses both in stream and out of stream.